Leather lubrication



United States Patent 3,035,882 LEATHER LUBRICATION George H. Von Fuchs, 278 Concord Ave, Belmont 78, Mas. No Drawing. Filed June 3, 1958, Ser. No. 739,457 13 Claims. (Cl. 8-94.22)

ThE fiHVCDllOII of the present application relates to leather lubrication and is particularly concerned with a novel process for lubricating leather and the novel products thereby obtained.

It is an object of the present invention to provide a process for obtaining well lubricated leather with very small amounts of lubricants.

Another object of the present invention is to provide a process for lubricating leather in which wetting and emulsifying agents are not necessary.

Another object of the present invention is to provide a process for lubricating leather which makes possible the prevention of over-lubrication.

..-A further object of the invention is to provide a process I for lubricating leather that results in the production of strong leather.

Another object of the present invention is to produce leather which is permanently lubricated and which will dry soft even after repeated rewetting.

Still another object of the present invention is to provide a process of the character described that is inexpensive and convenient to use.

A further object of the invention is to produce a welllubricated, strong leather which is well suited for further treatment.

When unlubricated wet leather is allowed to dry it will become hard and stiff because of cohesion of the leather fibers. The principal purpose of such a leather lubricating process as conventional fatliquoring is to prevent or control this cohesion so that the leather will be strong and of the desired degree of flexibility or softness.

Commercial fatliquors contain one or more animal and/ or vegetable oils together with one or more wetting or emulsifying agents of the types that promote oil-in-water emulsions. These agents have little or no lubricating value of their own. They act merely as coupling agents that assist the emulsified oils to enter the wet leather and coat the leather fibers, thus preventing cohesion thereof when the leather dries. Particularly with the stronger emulsifiers this action is apparently reversible. In consequence, when the dried, fatliquored leather is rewetted by water the emulsifier facilitates the displacement of the leather lubricant from the fiber surfaces. When this happens the leather will dry hard even though large quantities, e.g. l5%20%, of lubricant have been used.

In stuffing leather wet leather is simply milled with oils, molten greases and waves to produce a virtually saturated leather which is frequently greasy to the touch and is not generally receptive to finishes or various other surface treatments.

By the novel method of the present invention a suitable lubricant is deposited on the leather fibers without employing wetting or emulsifying agents. Further, the lubricant deposition may be so controlled in amount and location that desired properties in the leather can be readily and consistently obtained.

The lubricants primarily used in carrying out the process of the present invention are water-insoluble, oil-soluble, polar compounds. These are conveniently introduced into wet leather as single phase lubricating compositions consisting of solutions of such lubricants in water-immiscible solvents. Such solvents should have an evaporation rate lower than that of water and yet should be so volatile that they will evaporate completely from the leather within. a reasonably short time after use.

3,035,882 Patented May 22, 1962 In the following example there is described the preferred method of carrying out the present novel lubrication process using shoe-upper leather which has been conventionally chrometanned.

EXAMPLE 1 A piece of the leather while still wet from the washing after tanning is wrung, i.e. passed between rollers that are so set or held as to squeeze out some of the water, to bring the water content of the leather down to 60%. The leather is then dipped in a solution containing 8% of glyceryl monooleate dissolved in a petroleum naphtha having a boiling point between 365 F. and 399 F. and a flash point of F. or above. After such dipping, the again saturated leather is preferably covered for one hour or more to allow time for the lubricant to penetrate to and coat the leather fibers and is then dried by pasting in the conventional manner. While in this example the leather after drying contains only about 1% of lubricant, it is of uniform softness and temper and has a strength equal to or greater than substantially identical leather lubricated by conventional fatliquoring.

Instead of dipping the wrung leather as described in Example 1, the lubricant solution can be applied in pther ways. This is illustrated in Example 2.

EXAMPLE 2 A piece of wet, conventionally chrome-tanned shoeupper leather is wrung to bring the water content thereof down to 55%. A solution containing 10% of glyceryl monooleate dissolved in a petroleum naphtha having a boiling point between 365 F. and 399 F. and a flash point of 140 F. or above is then applied to the grain side of the wrung leather and brushed into the leather. Enough solution is used to substantially saturate the leather surface. The treated leather is covered for at least one hour and is then dried according to the usual pasting procedure. The resulting lubricated leather has a good temper and is quite full. 1 l

In the following examples there are described variant procedures for carrying out the present novel leather lubricating process.

EXAMPLE 3 A piece of wet, tanned sole leather is wrung to a. water content of 51%. It is then dipped in a 5% solution of glyceryl monooleate in a petroleum naphtha of the same type used in Examples 1 and 2. About 18% of the solution is picked up by the leather. After drying in the air the leather will contain about 0.9% ofthe lubricant and will have all of the desirable properties of a well-lubricated sole leather containing several times as much of the lubricants conventionally used for sole leather.

EXAMPLE 4 If the procedure of Example 3 is repeated except that the naphtha contains in solution 2.5% of glyceryl monooleate and 2.5% of a. low-viscosity mineral oil, it will be found that the wrung sole leather picks up about 20% of its weight of the solution. After air drying the leather will be similar in properties to that resulting from the procedure of Example 3 but somewhat softer.

EXAMPLE 5 A piece of wet shoe-upper leather that has been chrometanned and subsequently heavily retanned with a lignosulfonate solution is treated according to the procedure described in Example 1. The resulting lubricated leather when dried is soft and mellow and very much stronger than such leather lubricated by conventional fatliquoring.

EXAMPLE 6 A piece of wet, chrome-tanned leather after wringing s,oss,ssa

. 3 i to about 60% water content isfdipped in a solution of sorbitan monooleate in petroleum naphtha and dried. The resulting lubricated leather is soft and mellow.

EXAMPLE 7 petroleum naphtha having a boiling range between 365' F. and 399 F. and a flashpoint of 140 F. or above. Such naphthas are extensively used, e.g. for odorless paint thinners and insecticide bases. They are water-immiscible and non-toxic and also substantially colorless and odorless so that no stains or residual odor will be left on or in the leather. At the same time they are quite inexpensive and are therefore economical to use.

Although such solvents are preferred for forming solu tions of leather lubricants for use in carrying out the proces of the present invention, other water-immiscible solvents, for example hydrocarbons such as kerosene, xylene and decahydronaphthalene, may be employed with satisfactory results. In addition to being water-immiscible, solvents for use in the present process should have an evaporation rate substantially lower than that of water so that they remain in the leather until the water is removed in drying and yet should be readily volatile at normal leather drying temperatures. Consequently, preferred solvents will have boiling ranges not substantially in excess of about 500' F. Any solvent meeting these requirements can be used with reasonably satisfactory results, due care, of course, being taken with toxic .solvents and those presenting fire or explosion hazards.

As mentioned above, the lubricants used in carrying out the present process should be water-insoluble, oil-soluble, polar materials. Obviously, the material should be substantially insoluble in water to prevent loss of lubricant if the lubricated leather is wet. Oil solubility is also necessary if the material is to be applied in a hydrocarbon solution. The material should in addition be rather strongly polar as it will then tend to be firmly bound to or adsorbed on the leather fibers thus providing permanent lubrication. It will be evident that by choice of more or less strongly polar lubricants it is possible to have some control over the adsorption. Suitable lubricants include glyceryl monostearate and monooleate and sorbitan monooleate, mentioned in the foregoing examples, as well as water-insoluble, oil-soluble, alkyl phenyl ethers of polyalkylene glycols, long chain alkyl and alkenyl substituted succinic acids, a number of metallic soapssuch, for example, as the oleates and stearates of calcium, aluminum, and magnesium, and long chain alkyl aryl sulfonates.

In Example 4 the lubricant used consists of a mixture of glyceryl monooleate and a mineral oil. Mixtures of the polar lubricants mentioned above with an equal or somewhat greater amount of a mineral oil are found to be substantially as elfective as larger amounts of such lubricants without mineral oil. While the exact mechanism is not entirely clear, it appears that the oil-soluble, polar lubricants are able to anchor themselves to the leather fibers and at the same time bind the mineral oil. As a result of using such blends, in many cases the desired degree of lubrication can be obtained with extremely small amounts of polar lubricant. Instead of a true mineral oil, any non-volatile, synthetic hydrocarbon lubricant may be used. In fact, many of the lubricants employed in conventional leather lubrication may be used instead of mineral oil. Since, however, they are more expensive and do not produce significantly superior results, their use will not be attractive in most cases.

When using a polar lubricant alone it is preferred to carry out the process in such a way that the lubricated leather after drying will contain about 1% lubricant.

Good results have been obtained, however, where the polar lubricant content of the dried leather was in the range from about 0.5% to 1.5%. When employing mixtures of polar lubricants and mineral oil or other non-volatile lubricant the percentage of polar lubricant can be reduced to from about 0.25% to about 0.75% and an equal or somewhat greater amount of hydrocarbon lubricant used therewith. It will be recognized that the amount of lubricant employed will vary in accordance with the type of leather used, its intended purpose and the degree of softness and flexibility desired. Larger amounts of lubricant increase the softness of the leather. Accordingly where a firm, relatively stiflE leather is wanted the lubricant content should be nearer the lower limits of the above-mentioned range than when a very soft, pliable leather is desired.

As mentioned above, the degree or extent of lubrication necessary will vary with the type of leather, its intended use, and the properties desired therein. It is evident that the lubrication process of the present application is adapted to provide the desired amount of permanent lubrication in a convenient way. The method is applicable to any type of leather. As indicated in the foregoing examples, the leather may be chrome tanned only, chrome tanned and then retanned, or tanned with vegetable tanning agents only. It has also been found that leather tanned with synthetic tanning agents only or chrome tanned and then retanned with synthetic resins or vegetable tannins may be easily and effectively lubricated by the present process. Zirconium tanned leather has also been effectively lubricated by the present process. Splits as well as buffed and full grain leathers are usable. In fact, extensive experiments indicate that the present process is useful with leather of all types.

Example 1, above, describes the preferred method of carrying out the present novel lubrication process. It will be understood, however, that many variations from the procedure there outlined may be employed without departing from the essence of the present invention. Examples, not intended to be comprehensive, of such variations are set out below.

Wringing Wet leather as it occurs in normal tanning procedure contains about to water. In the present process it is necessary to remove some of this water to make possible the absorption of the lubricant solution. The amount of water to be removed will depend upon the amount of lubricant it is desired to add to the leather and the lubricant concentration of the treating solution. Passing the wet leather through rolls, at least one of which is usually covered with cloth or other absorbent material, is the most convenient way of removing water from the leather. In such wringing, the amount of water removed is controlled by proper adjustment of the load on the upper roll. The desired amount of water can be removed, however, in other ways as, for example, by pressing between absorbent surfaces or even by carefully controlled drying. In any event, it has been found that for most purposes the water content should be reduced to between about 45% and 60%, greater reduction often resulting in such large pickup of lubricant solution that the leather may take an inordinate time to dry and, unless quite dilute lubricant solutions are used, may be overlubricated. If the water content is reduced below about 33% some cohesion of the leather fibers may take place. Less reduction in water content will usually result in insufiicient penetration of the lubricant solution so that the leather is not adequately lubricated.

Solution Application As pointed out above, the solution of polar lubricant in water-immiscible solvent may be applied to the wrung leather by dipping or brushing. Other methods, such as spraying, can be used and numerous variations on these steps may be employed. For example, there may be sucs,ose,ssa

cessive applications on one or both sides of the leather and with, if desired, solutions of different lubricant concentration. By variation in the relative amounts of lubricant applied in solution to the two sides of leather that has been properly wrung the location of the lubricant in the leather can be somewhat controlled. In many cases more lubricant and greater lubricant penetration is desired in the grain side. This can be achieved by applying a more concentrated solution of lubricant to the grain side than to the flesh side. After application of the lubricant solution or solutions it is usually desirable to cover the leather and permit it to stand for an hour or more before drying. This period of storage permits the polar lubricant to coat the leather fibers more evenly and extensively. However, this storage period may be omitted when satisfactory results are obtainable without it. When exceptional softness and pliability is desired, such as in case of garment and glove leathers, it is advisable to mill the leather after application of the lubricant solution. Such leathers are also normally wrung out more completely (down to about 45% water) before the application of the solution. To avoid overlubrication, the lubricant solution used should be rather dilute.

Drying Leather lubricated by the present novel process may be dried in any convenient way, at the temperatures conventionally used in drying leather. Both pasting and toggling, as well as loft drying have been satisfactorily used. The drying proceeds without difficulty and may be more readily accomplished in some cases than drying of the same leather when normally fatliquored. When pasted, leather lubricated by the present process dries with an exceptionally smooth grain.

The present novel lubrication process produces leathers of fine quality and unique usefulness. Since the amounts of lubricant employed are so low these leathers are extremely porous and thus have much better insulating properties than stuffed leathers, in which the leather pores are substantially filled with wax and g ease, or even normally fatliquored leathers which may contain as much as 15%-20% of lubricant and emulsifier. The small amounts of lubricant used also permit bufiing of even the softest leathers without the difliculties encountered with heavily fatliquored leathers. Finishing, likewise, is easier with leathers lubricated by the present process since there is no excess lubricant to interfere with the adhesion of the finish coats. Also, of course, the high porosity of the leathers permit deeper penetration and better anchoring of the finishes. Such leather is also very suitablefor the making of shoes by cementing or vulcanizing since t g eater porosity of the leather and its dom from excess oil permits much better bonding.

f great importance is the fact that leathers lubricated by the present processieven after repeated rewetting with water, and drying, always dry soft and flexible. The

'durability of leather goods formed therefrom is thus greatly increased. As previously pointed out, the strength of such leathers is also excellent, being at least as great and often greater than that of identical leathers lubricated by conventional fstliquoring.

As hereinabove described, it is seen that the present process is uncomplicated, requires no modification of the normaltanningordryingprocedureandisinexpensive. The amounts of polar lubricants used are so much less than the amounts of lubricants used in fatliquoring or smflingthstconsiderablyhigherprices csnbe'psidfor the former without increasing the total cost of materials.

I claim:

1. A process for lubricating leather which comprises reducing the water content of wet, tanned leather to between about 45% and 60%, then applying to said leather a single phase lubricating composition consisting of a solution of a water-insoluble, oil-soluble, polar lubricant in a water-immiscible, organic solvent having an evaporation rate lower than that of water but readily volatile at nor mal leather drying temperatures, said solution containing an amount of said lubricant adequate to properly lubricate said leather, and then drying said leather.

2. A process as set forth in claim 1 in which said solution contains from about 2.5% to about of said polar lubricant.

3. A process as set forth in claim 1 in which such a concentration of polar lubricant is used in said solution that said leather after drying will contain from about 0.5% to about 1.5% lubricant.

4. A process as set forth in claim 1 in which said solution also includes a hydrocarbon lubricant.

5. A process as set forth in claim 1 in which said solution contains from about 5% to about of a mixture of polar lubricant and hydrocarbon lubricant.

6. A process as set forth in claim 5 in which said hydrocarbon lubricant is present in said solution in an amount at least equal to the amount of p'ola r lubricant.

7. A process as set forth inclaiin 6 in which such a concentration of lubricants is' used in said solution that said leather after drying will contain from about 1% to about 3% lubricant.

8. A process for producing permanently lubricated and strong leather which comprises applying to wet, tanned leather a single phase lubricating composition consisting of a solution of a water-insoluble, oil-soluble, polar lubricant in a water-immiscible, organic solvent having an evaporation rate lower than that of water but readily volatile at normal leather drying temperatures, said solution containing an amount of said lubricant adequate to properly lubricate said leather, and drying said leather.

9. A process as set forth in claim 8 in which the water content of said leather has been reduced to between about and before application of said solution.

10. A process as set forth in claim 8 in which said leather has been wrung before application of said solution.

11. A process as set forth in claim 9 in which said solution contains from about 2.5% to about 10% of said polar lubricant.

12. A process as set forth in claim 9 in which such a concentration of polar lubricant is used in said solution that said leather after drying will contain from about 0.5% to about 1.5% lubricant, and said solution also includes a hydrocarbon lubricant.

13. A process as set forth in claim 9 in which said solution contains fromabout 5% to about 20% of a mixture 55 of polar lubricant and hydrocarbon lubricant.

References Cited -in the file of this patent UNITED ,smras PATENTS OTHER REFERENCES Progress in Leather Science, p. ,631.

Progress in Leather Science, 1920-1945, British Leather Manufacturer's Research London 1948, age 42,1, 

1. A PROCESS FOR LUBRICATING LEATHER WHICH COMPRISES REDUCING THE WATER CONTENT OF WET, TANNED LEATHER TO BETWEEN ABOUT 45% AND 60%, THEN APPLYING TO SAID LEATHER A SINGLE PHASE LUBRICATING COMPOSITION CONSISTING OF A SOLUTION OF A WATER-INSOLUBLE, OIL-SOLUBLE, POLAR LUBRICANT IN A WATER-IMMISCIBLE, ORGANIC SOLVENT HAVING AN EVAPORATION RATE LOWER THAN THAT OF WATER BUT READILY VOLATIEL AT NORMAL LEATHER DRYING TEMPERATURES, SAID SOLUTION CONTAINING AN AMOUNT OF SAID LUBRICANT ADEQUATE TO PROPERLY LUBRICATE SAID LEATHER, AND THEN DRYING SAID LEATHER. 